Abstract

Cardiovascular diseases are among the most important causes of death in thedeveloped countries. These diseases are partly caused by too high cholesterolconcentrations in the blood. Avena sativa, oat, is the most common spieces of the genus Avena, and produced in huge amounts worldwide. Oats have been shown to have cholesterol-lowering properties since the 1960s. This property was originally attributed to the ß-glucans, however, it has also been observed that other compounds, which are soluble in organic solvents (not ß-glucans), are able to lower the cholesterol concentration in the blood in rats as well as in humans.

The aim of this thesis has been to obtain a better understanding about therelationship between the cholesterol lowering effect (CLE) and compoundsnaturally present in oats (besides ß-glucans).

Initially, avenanthramides (AVAs), which is a major group of phenolic compounds present in oats, were detected and quantified in order to search for any relationship between the contents of AVAs in oats and a CLE. However, there was no obvious relationship, and it seems unlikely that the AVAs contributesignificantly to the CLE. During this study, it was necessary to prepare AVAs bysynthesis, as their isolation from oats as pure compounds in larger amounts israther complicated. Fourteen AVAs, whereof six are natural products, weresynthesized, and used as standards for the analytical work as well as for in vitroassays. The three most prevalent AVAs in oat, avenanthramides (1), (2), and (3)were evaluated in vitro for their ability to prevent oxLDL-induced lipidaccumulation in murine macrophages. However, the pre-incubation of the macrophages with the three AVAs (1), (2), and (3) did not alter the mRNAexpression of scavenger receptors or lipid transporters of the macrophages.

Bio-assay guided fractionation was used to find the fraction of oat with thestrongest CLE. Oat extracts were fractionated and the fractions were tested in vivo. The fraction rich in phytosterols showed the best CLE. However, anothercompound, 13-HODE, was also present in the fractions showing CLE. Thus, itwas not possible to link the CLE to a specific compound or compounds.